How does exercise help you lose weight if muscle builds on fat?

the bigger your muscle becomes, bigger consume of energy after exercise. After aprox. 20 min of exercise you will use your energy from the fat, and if your intake of energy is less than your consume, is just math. Muscle doesn't build fat (it burns it) and muscle weighs more than fat. If you became a body builder and had good muscles and then years later didn't bother to keep up your exercise regime this is when the muscle would turn to fat. Muscle cannot turn to fat. But if you do not continue working it you will lose muscle mass and burn less calories. If you do not eat less or exercise more to compensate for this reduction in muscle mass than you will gain weight back in the form of fat.